The amount of time a cellular handset can operate on a fully charged battery is in conflict with the increasing consumer demand for more features and smaller handsets. In an attempt to keep up with the power requirements brought about by these consumer demands, the cellular handset industry has turned to advanced higher capacity lithium ion battery technology. However, a trade-off exists in that an advanced lithium ion battery can be discharged to a lower operating voltage than typical lithium ion batteries. The lower operating voltage is incompatible with existing power amplifier (PA) technology that is used in some of the basic building blocks of cellular handset circuitry. In order to solve this lower voltage incompatibility issue, the cellular handset industry has turned to Direct Current (DC) to DC converter technology to boost the voltage of advanced lithium ion batteries to a level that is compatible with existing PA technology. Moreover, it is widely recognized that DC to DC converter technology is generally much more efficient at regulating output voltage than typical linear voltage regulator technology. Thus, DC to DC converters offer increased efficiency that can provide longer handset operation time or smaller handsets while stepping up the voltage for compatibility with existing PA technology.
Low current voltage boosting is commonly accomplished with a range of charge pump architectures that gradually charge a holding capacitor to twice the input voltage from a source such as a lithium-ion battery. More evolved versions of charge pump architecture can regulate output voltages. However, these evolved versions of charge pump architecture are generally less efficient.
When higher load currents are needed, conventional boost converters that include a power inductor can be used. Inductor based boost converters can produce output voltages that are either equal to or greater than the input voltage. Some architectures, referred to as buck-boost, can generate output voltages that can either be smaller or greater than the input battery voltage. However, the level of ripple or Alternating Current (AC) variation present on the output DC voltage is always too large and causes spectral splatter at the output of the power amplifier. To reduce the level of such ripple beyond what can be done with filtering, the more conventional inductor based boost converter is followed by either an inefficient linear voltage regulator or by a buck regulator. However, even when an inductor based boost regulator is followed by a buck regulator, the overall efficiency is poor because the combined or cascaded efficiency is equal to a multiplication of both the boost and buck efficiencies. Moreover, two power inductors are needed in such architectures, which results in increased design complexity and added expense. As a result, there remains a need for a low cost, small footprint, high efficiency DC to DC converter having an excellent low ripple output voltage.